You can customise the pricing items dropdown which is available when creating an estimate or invoice. This list of items is designed to be the services or products that you provide. For example, a 'Standard service' being listed at £50.00.
How to add a pricing item:
First, go to your system settings.
In the list of general settings click 'Pricing items'.
You will see a form on the left-hand side and a list of existing pricing items on the right-hand side. You can add your new pricing item on the left and it will appear on the right side when you click 'Add pricing item'.